The Retention Date will normally be 12 months from today.
The Retention Invoice No is normally the original Invoice number with an 'A' or 'B' added to the end.
The value of the Retention goes against 'Amount' and is a Negative.
Click OK, the entry will be made.
Continue on and allocate any payments against the remaining invoices.

Here you can see the Retention entries (PR) and a date in the Retn. Date Column.

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